“Nobody is listening to your telephone calls,” Mr. Obama said when the news broke.

But as experts on American intelligence knew, that was not the whole story. It left out what N.S.A. officials have long called “incidental” collection of Americans’ calls and e-mails — the routine capture of Americans’ communications in the process of targeting foreign communications.

Vision
is often incorrectly compared to the operations of a camera. Unlike a
camera, however, the visual system is able to create a
three-dimensional representation of the world from the
two-dimensional images on the retina. In addition, an object is
perceived as the same under strikingly different visual conditions.

A
camera reproduces point-by-point the light intensities in one plane
of the visual field. The brain, in contrast, parses scenes into
distinct components, separating foreground from background, to
determine which light stimuli belong to one object and which to
others. In doing so it uses previously learned rules about the
structure of the world. In analyzing the incoming scream of visual
signals the brain guesses at the scene presented to the eyes based on
past experience.

This
constructive nature of
visual perception has only recently been fully appreciated. Earlier
thinking about sensory perception was greatly influenced by the
British empiricism philosophers, notably John Locke, David Hume, and
George Berkeley, who thought of perception as an atomistic process in
which simple sensory elements, such as color, shape, and brightness,
were assembled in an additive way, component by component. The modern
view that perception is an active and creative process that involves
more than just the information provided by the retina has its roots
in the philosophy of Immanuel Kent and was developed in detail in the
early 20th century by the German psychologists Max Wertheimer, Kurt
Koffka, and Wolfgang Koehler, who founded the school of Gestalt
psychology.

The
German term Gestalt
means configuration or form. The central idea of the Gestalt
psychologists is that what we see about a stimulus--the perceptual
interpretation we make of any visual object--depends not just on the
properties of the stimulus but also on its context, on other features
in the visual field. The Gestalt psychologists argued that the visual
system processes sensory information about the shape, color,
distance, and movement of objects according to computational rules
inherent in the system. The brain has a way of looking at the world,
a set of expectations that the rides in part from experience and in
part from built-in neural wiring.

About Me

Student of the law of evidence, evidence, inference, and investigation. Sometimes writes books. Sometimes writes articles. Sometimes tinkers with computer programs to support the marshaling of evidence for legal activities such as trials and pretrial discovery and investigation. And sometimes takes photographs.